type invariants assertions

[zpdDG4gta8XKpMCd]

closed in favor of #16605

in my code i often use, let's call them, type invariants assertions:

function mustBe<T>(_: () => T): void {}
interface A {
    isThat: true;
    text: string;
}
interface B {
    isThat: false;
    value: number;
}
type C = A | B;
declare const C: C;
mustBe<true>(() => C.isThat); // <-- type error as expected

now i wish i could do type invariant assertions without emitting any useless code, making it a zero cost abstraction:

makesure C.isThat sameas true;

where makesure is a new TS syntax/construct that participates in type checking, but doesn't get emitted

few more examples

makesure typeof c.isThat subtypeof boolean
makesure MyClass subtypeof BaseClass
// ...

[gcnew]

I use type aliases for pseudo static asserts.

type HasType<T, Q extends T> = Q;

type StaticAssert1 = HasType<true, A['isThat']> // OK
type StaticAssert2 = HasType<true, C['isThat']> // Error as expected

[mhegazy]

duplicate of #16605?